\
What Your Experiment Showed
This is an easy experiment to do. But to understand what
happened is not so easy.
Here's a quick explanation:
o
'
.
You know that when a circuit is broken, electricity doesn't flow.
And you know that turning a switch to the oFF position breaks
the flow of electricity in that device.
The electricity caused chemical changes both in the salt
water and in one of the brads.
But think of all the lights and appliances in your home. when
we turn one of them off, why don't all the others go off, too?
The greenish-gray sludge comes from a chemical
combination of the metal in the brad with part of the
salt in the water.
The following experiments will show why.
The bubbles that form on the other brad are hydrogen
gas, the lightest gas in the universe. The hydrogen came
from splitting the water molecules; water is made of the
gases hydrogen and oxygen.
You'll find a more complete explanation later in the book.
As you saw, in this experiment electric current brought about a
chemical change. Using electricity to split moleculeJ and make
chemical changes is calle d electrolysis, which means "loosening
or splitting with electricity. "
Electrolysis was discovered very shortly after the invention of
the battery. Today, electrolysis is often used by scientists to make
or study new chemicals. It is also widely used to make the
chemicals that are used in our factories and industries.
Another common use is to put a metal coating on an object.
This is called electroplating. If you had used a siiver salt instead
of table salt in the water, the brad would have been plated with
silver when you passed electricity through it.
24
light Bulbs in Series ond in Porollel
A. Experiment with Two Light Bulbs in Series
1. Add the second light bulb in your kit to your circuit board
setup. You'll also need to insert a new connector, connector
C, between the bulbs,
Follow the illustration and the circuit
diagram (Fig. 10). Putting two light bulbs in a row like this
is called putting them in series.
2. Switch the switch to ON. What happens to the light bulbs?
o
J.
compare the brightness of each bulb in the series circuit
to the brightness of one bulb alone. Do this by keeping
the switch ON and then touching one end of a wire to
Connector B and the other end to Connector C. You have
created a short circuit around Bulb 2. (An electrician
would say that you "sftorted out" Bulb 2.) The electricity
bypasses Bulb 2 and goes through Bulb 1 only. Which is
brighter-a single bulb in a circuit, or 2 bulbs in series?
4. with the switch still on, unscrew Bulb 2 from the series
circuit. What happens?
5. Put Bulb 2 back in its socket and switch everything
oFF.
25
B. Experiment with 2 Light Bulbs in Parallel.
1. Make a new setup with the 2light bulbs. Take the wires
Bulb
1
ends out of Connector C and remove this connector. Put
one wire into Connector A and the other into Connector
B, exactly the way the diagram shows (Fig. 11).
Bulb 2
Connector C
Bulb
1
Bulb 2
Connector
Connector
Switch..,.''
Fig. 10
B
'
,..,,'
Connector
Battery Holder
What Your Experiment Showed
You should have found the following things about two bulbs
wired in series:
Two light bulbs in series are not as bright as one light
bulb alone. This is because the "push" that the batteries
give to the electric current remains the same, but now
the current has to light up two bulbs .
.
26
As you can see from the circuit diagram, if you remove a
bulb, you break the circuit. And so the other bulb also
goes out. It doesn't matter which one you remove. The
other also goes out.
Fig.
11
Connector B
Bulb
1
Connector
A
Switch Connector
27
Putting two light bulbs side by side in
wiring them in parallel.
a
circuit like this is called
2. switch the switch to oN. what happens to the light bulbs?
3. Again, compare the brightness of each bulb in the parallel
circuit to the brightness of one bulb alone. Do this by
disconnecting both Bulb 2 wires from the connectors.
which is brighter-a single bulb in a circuit, or two bulbs
in parallel? which is brighter, two bulbs in paraller, or
two bulbs in series?
4. Reconnect Bulb 2. with the switch still on, unscrew Bulb
2 from the parallel circuit. What happens?
5. Put Bulb 2 back and switch everything
OFF.
What Your Experiment Showed
Look carefully at your circuit board and at the circuit diagram.
At first they may not look the same at all. But if you took at
them carefully, you will understand how they show the same
kind of circuit. The labeling on the circuit diagram should help
you.
Notice that in a parallel circuit, the path of the electricity splits
in two, and then join the two paths again. Some of the current
goes in one path, through Bulb 1. The rest goes in the other
path, through Bulb 2. This is very different from a series circuit,
where there is only one path for the electricity to follow.
You should have noticed the following things about a parallel
circuit:
.
.
Bulbs wired in parallel are brighter than bulbs wired in
series!
when two light bulbs are wired in parallel, each butb is
nearly as bright as one bulb wired by itself.
(Surprisingly, in a parallel circuit like this one, each of
the branches draws the same amount of electricity
the one path of an ordinary circuit.)
.
as
when you remove one bulb from one branch of a parallel
circuit, the other branch of the circuit is not broken. So
the other bulb stays lit. This is why appliances in your
home are wired in parallel, not in series.
Some of the electricity in the circuit is wasted in heating up the
wires and the connectors. If there were no waste, each light
bulb in the parallel circuit would be just as bright as a single
Iight bulb.
You don't get the extra brightness for free. The circuit is now
lighting two bulbs at nearly full brightness, so it is using two
times the amount of current as a circuit with only one bulb.
The batteries will wear out more quickly.
C. Make a Two-Way Switch
with a small change in your parallel circuit, you can make a
two-way switch. The switch will turn on either bulb, but not
28
29
I
Botteries in Series ond in Porqllel
both at once.
1. Make a new temporary connector (Connector D) on the
other side of the switch from connector A. Take the wire
from Bulb 2 oul of Connector A and insert it in Connector
D. Follow the diagram to make sure everything is correct
(Fig.12). And check under the circuit board to make sure
the legs of the brads are not touching!
You now have a two-way switch.
A. Make a Battery Tester
1. Remove one of the bulbs and holders from the circuit
board.
2. Take the brass strip with the two holes in it. put the end
of a bulb wire into a hole and wrap the end around the
brass strip so that it makes a good electrical contact.
3. Put the other bulb wire end between the legs of a brad.
wrap the wire end around the brad
a good electrical contact.
Bulb
so
that it, too, makes
Your tester is now complete. It should look like the one in the
drawing (Fig. 13a).
1
Connector
B
B. Test with One Battery
1. Take a battery out of the battery holder. place the flat
Connector
D
bottom of the battery on the brass strip. Touch the bump
I on the top with the brad, the way the drawing
(Fig. 13b). What happens?
Switch
.ii, ,
...i.
shows
,
Connector
Battery Holder
Fig. 12
Connector B
Bulb
Brass
Fig. 13a
Fig.
13b
striP
2. Turn the battery upside down so that the bump is on the
. brass strip. Touch the flat end with the brad. What
1
happens?"
Connector A
30
3l